check: Update the flutter_version check to follow upstream

[rajveermalviya]

Since https://github.com/flutter/flutter/commit/e45fd36aa the flutter tool now uses a combination of git commands, instead of using the result of git describe to generate the version string.

So, we update the check to use the same commands here, and then do some transformations to match the string from the flutter tool: https://github.com/flutter/flutter/blob/9f383e099/packages/flutter_tools/lib/src/version.dart#L1162

Fixes: #1851